#include<iostream>
using namespace std;

struct TreeNode {
     int val;
      TreeNode *left;
      TreeNode *right;
      TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};

class Solution {
public:
    TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
        if(root == NULL)return NULL;

        if(root->val> p->val && root->val>q->val){
            return lowestCommonAncestor(root->left,p,q);
        }

        if(root->val< p->val && root->val<q->val){
            return lowestCommonAncestor(root->right,p,q);
        }
        return root;
    }
};